Groundbreaking federal programs including CMS's quality initiatives and AHRQ's quality and safety portfolio have increased transparency and improved the value of healthcare. The Patient Protection and Affordable Care Act have prioritized community and population health as the critical next step in the quality movement. As a result, the National Quality Forum and the Institute of Medicine have focused efforts on understanding how best to improve population health, and the Department of Health & Human Services has created a National Quality Strategy. While population health has been defined conceptually, no accountable geographic unit has been defined and thus standardized measurement of health indicators across communities cannot be measured and compared. The overall goal of this proposal is to empirically derive novel health care coalitions and their corresponding catchments that can be used to measure progress toward the achievement of population health. We will use existing Ambulatory Care Sensitive Conditions (ACSC, called Prevention Quality Indicators), the soon to be released Emergency Department Prevention Quality Indicators, and a number of Emergency Care Sensitive Conditions (ECSC) to paint a compelling portrait of the healthcare system's management of the population's acute healthcare needs. We will first identify healthcare coalitions (HCC) and their corresponding geographic catchments that empirically represent acute healthcare utilization across the United States. Then, we will evaluate the ability of healthcare coalitions (HCC) to detect meaningful variability of health indicators to facilitate comparative reporting between coalitions. Finally, we will measure variability in prevention quality indicators across healthcare coalitions and publicly disseminate statistical code and geographic shapefiles for healthcare coalitions and catchments. Healthcare facilities that share patients from overlapping neighborhoods have a shared responsibility for the needs of those who look to them in their time of need. To date, it has been difficult to measure the quality of care delivered to the population by local and regional healthcare delivery systems. The work proposed here will develop an empirically defined geographic denominator that describes the population for which groups of hospitals share the responsibility of population health, and this work will facilitate cooperation across the multisectoral health system.